India, April 23 -- The most serious cyberattacks in the UK are now carried out by hostile nations including Russia, Iran and China, the head of the UK's National Cyber Security Centre said in a speech on Wednesday.

Richard Horne, the head of the National Cyber Security Centre (NCSC) - part of the UK's signals intelligence agency GCHQ - warned that the UK is living through "the most seismic geopolitical shift in modern history."

British businesses, he said, need to prepare themselves to defend against cyberattacks because the UK could be targeted "at scale," if it became involved in an international conflict.  In recent months, authorities in Sweden, Poland, Denmark and Norway have all warned that hackers linked to Russia have targe...